I just installed Debian testing (2.6 kernel) on a Dell Dimension 8200. It has a "Davicom Semiconductor, Inc. 21x4x DEC-Tulip compatible 10/100 Ethernet (rev 31)" network card. The "dmfe" and "tulip" kernel modules are always both loaded when the computer starts up; and the network card works briefly and then doesn't work. I can fix it by manually doing this as root:
# ifdown eth0
# rmmod dmfe
# rmmod tulip
# modprobe dmfe
# ifup eth0

But this only lasts until the next reboot. Does anyone know why there is this problem and if there is a permanent solution? Thanks.

If I understand correctly, tulip and dmfe conflict, so when you modprobe dmfe, tulip isn't reloaded?

You can blacklist tulip to prevent it from loading. List "tulip" in the file: /etc/hotplug/blacklist and it won't be loaded by hotplug when you reboot. If you are using udev instead of hotplug, list "tulip" in /etc/modprobe.d/blacklist to prevent it from loading.

If the above isn't the problem and there is something weird about removing and reloading both modules, you can automatically run the commands you are using during boot up as a work around. Edit the file /etc/rcS.d/S40networking. Just under where it says "Configuring netwrok interfaces...." add your commands: